1. Field of the Invention
This invention relates generally to paved surfaces, and more particularly, but not by way of limitation, to a fiber modified layer having improved fatigue or crack resistant properties.
2. Description of the Related Art
One of the most adaptable tools in road maintenance is slurry mixture. Slurry mixture is a polymer-modified cold-mix paving system that can remedy a broad range of problems on today's streets, highways, and airfields. Slurry mixture begins as a mixture of dense-graded aggregate, asphalt emulsion, water, additives, recycled materials, and mineral fillers. While conventional slurry seal is used around the world as an economical treatment for sealing and extending the service life of both urban and rural roads, slurry mixture has added capabilities, due to the use of high-quality, carefully monitored materials, including advanced polymers and other modern additives. Slurry mixture is recognized as a cost-effective way to treat surface wheel-rutting problems and a variety of other road surface problems. Slurry mixtures are hereafter referenced only as slurry mixture.
Slurry mixture is made and applied to existing pavements by a specialized machine, which mixes the components on site, and spreads the mixture onto the road surface. Materials are continuously and accurately measured, and then thoroughly combined in the slurry mixture machine's mixer. As the machine moves forward, the mixture is continuously fed into a variable-width “surfacing” box which can apply materials to the width of a traffic lane in a single pass. Alternately, specially engineered “rut” boxes, designed to deliver the largest aggregate particles into the deepest part of the rut to give maximum stability in the wheel path, may be used. Edges of the slurry mixture are automatically feathered. The new surface is initially a dark brown color and changes to the finished black surface as the water is ejected and the surface cures, permitting traffic within one hour in most cases. Continuous-load pavers utilize support units that bring the materials to the job site and load the machine while it is working, thus maximizing production and minimizing transverse joints.
Because slurry mixtures can be effectively applied to most surfaces, more area is covered per ton of mix, resulting in cost-effective surfacing. Traditional hot mix used approximately 165 lbs to 220 lbs of mixture to apply a 1.5 inch to 2 inch layer over a 1 square yard area. Conversely, slurry mixtures typically use 15 lbs to 30 lbs of mixture per square yard to provide a suitable surface. Slurry mixtures also create a new, stable surface that is resistant to rutting and shoving in summer. The mixture fills in cracks and surface imperfections. Because of its quick-traffic properties, slurry mixture can be applied in a broad range of temperature and weather conditions, effectively lengthening the paving season.
Slurry mixture begins with the selection of high-quality materials—asphalt emulsion, aggregate, emulsifiers, water, and additives—which must pass special laboratory tests, both individually and when combined, as a slurry mixture system. The International Slurry Surfacing Association's (ISSA) broad range of specialized mix design tests help to insure that the mixture has the desired slurry mixture characteristics.
To this end, although slurry mixture as currently practiced is an efficient road maintenance process, further improvements are desirable to a process for enhancing the fatigue resistant properties of paved surfaces. It is to such a fiber modified layer and method of selection and use that the present invention is directed.
Fibers have been used to enhance the crack resistance of paved layers like slurry seal and slurry mixture. The known art used a variety of fibers ≦0.25 inches in length to enhance the crack resistant properties of the layer. When tested for crack resistance like the ISSA Flexural Bend Test crack resistance was enhanced by using fibers.
While fatigue resistance, fracture energy, and fracture toughness of the mixture can be somewhat enhanced by ≦0.25 inch fibers, surprisingly crack resistance is generally unaffected.
Literature is laden with grid, mat, and lattice systems to assist crack resistance in road construction and rehabilitation. These processes have many drawbacks. They are expensive, require an extraordinary amount of fiber type materials and are difficult to construct.
Accordingly, it is desirable to provide a fiber modified layer with enhanced fatigue and crack resistant properties.